The invention relates to a heat exchanger, particularly for a heating or air conditioning unit in a motor vehicle.
In low-consumption vehicles because of the small amount of waste heat available, additional heat capacity is required in order to heat the passenger space and for the rapid elimination of a coating (ice or water) particularly on the windshield. For this purpose, it is known in heat exchangers constructed from flat tubes through which flows a heat transfer medium which emits heat in a heating situation, to provide, at least on the outer tubes, an additional heating in the form of PTC heating elements. However, the mounting of PTC heating elements of this type is highly complicated.
U.S. Pat. No. 6,124,570 proposes to replace individual tubes of the heat exchanger by PTC heating elements held between contact plates which at the same time make a heat-conducting connection to the adjacent ribs. This has the disadvantage that the structural adaption of the heat exchanger in order to receive PTC heating elements and the PTC heating elements themselves are very costly. For this reason, it may be that a combined heat exchanger of this type is more costly than a combination of a conventional heat exchanger with a separate PTC heater. Also, due to the construction space requirement for the PTC heating elements and the contacting of these, the power density of the heat exchanger is markedly impaired. The replacement of individual tubes of the heat exchanger may also be gathered from DE 44 36 791 A1 and DE 100 12 320 A1.
Furthermore, it is proposed in DE 198 58 499 A1, to design the flat tubes as multichamber profiles and to design at least one of the outer chambers in the form of an insertion groove for an insulated resistance wire, the walls of said insertion groove then being bent together in order to fasten the resistance wire. The resistance wire is inserted after the soldering of the heat exchanger. This has the disadvantage that a heat exchanger of this type requires special flat tubes and a large part of the electrically introduced heating capacity is absorbed into the coolant.
U.S. Pat. No. 6,178,292 B1 discloses a heat exchanger with an electrical heater which is arranged within a carrier element and which is pushed between two adjacent rib sets. In this case, the carrier element includes a pair of parallel plates, between which an electrical heating element is held and is contacted electrically. The electrical heater consists of a heating element and of an insulation element and has a multilayer construction through which a heating current passes essentially perpendicularly to the individual layers. Fastening elements, which run perpendicular to the carrier element and heater, are provided for the fastening. A heat exchanger of this type still leaves much to be desired, particularly as regards the multiplicity and number of parts and consequently the production costs of the heating body as a whole.